Millenium Mix-up?

A discussion on the T2T mailing list recently prompted the comment, “I hate to get technical, but the new millennium doesn’t actually begin until the year 2001…” Other members quickly responded, not understanding why the new millennium won’t begin on January 1, 2000. We felt that we should clarify.

A century lasts for 100 years and a millennium lasts for 1000 years. If we go back to the beginning of time and dates as we now use them, the first year was not “zero”, but rather 1AD. So, from the beginning of 1AD, one hundred years later would technically end in 100AD, and the new century would begin with 101AD.